Method for the synthesis of ureas

ABSTRACT

A method for the preparation of a group of variously substituted ureas is disclosed, these compounds being obtained by the pyrolytic decomposition of the alkali metal or alkaline earth metal carbamates corresponding to the expected ureas, the reaction taking place at a temperature of between 150° and 400° C under atmospherical pressures, and preferably under subatmospherical pressures, under which conditions the expected urea either sublimes or is distilled.

This invention relates to a method for the preparation of ureas having the formula: ##STR1## WHEREIN N = 2, 3, 4 and R and R' are hydrogen, alkyl or aryl radicals, cycloalkyl, aralkyl or alkaryl radicals, either substituted or unsubstituted, either saturated or unsaturated, by pyrolysis of the corresponding carbamates having the formula: ##STR2## WHEREIN Me is an alkali metal or an alkaline earth metal.

Such carbamates are prepared according to a method as disclosed in our copending patent application Ser. No. 639,442, filed Dec. 10, 1975.

The pyrolysis takes place according to the following reaction pattern: ##STR3## at a temperature comprised between 150° and 400° C, at ambient pressure or, preferably, under subatmospherical pressures: under these conditions, urea either distils or sublimes.

EXAMPLE 1

20 grams of C₆ H₅ NH--COOLi are placed in a test-tube having a tail pipe, to be inserted into an electric oven and in which there is a vacuum of 20 millimeters of mercury (abs.press.).

The oven is heated to 300° C and on the walls of the test-tube 14 grams of biphenylurea sublime, the residue being constituted by 6 grams of Li₂ CO₃.

EXAMPLE 2

20 grams of ##STR4## are treated as above at 350° C: 9 grams of N₁,N¹ - dimethylethyleneurea, the residue is 11 grams of K₂ CO₃. 

What we claim is:
 1. A method for the synthesis of a urea having the formula: ##STR5## wherein n is 2, 3, or 4, R is hydrogen, R' is phenyl and R" is lower alkyl, which consists in pyrolyzing the corresponding carbamate having the formula: ##STR6## wherein n, R, R' and R" have the meaning given above and Me is an alkali metal or an alkaline earth metal.
 2. A method for the synthesis of a urea as claimed in claim 1 wherein the pyrolysis is carried out at a temperature in the range between 150° and 400° C.
 3. A method of preparing biphenylurea which consists in pyrolyzing C₆ H₅ -NH-COOLi at a temperature of 300° C. at sub-atmospheric pressure.
 4. A method of preparing N₁, N¹ -dimethylethyleneurea which consists in pyrolyzing ##STR7## at a temperature of 350° C. and at sub-atmospheric pressure. 